Oxygen isotopes in corals and their use as proxies for El Niño
2014
Bokhari Friberg, Yasmin
El Niño and the Southern Oscillation (ENSO) have a great impact on global climate, often with disas-trous effects in many parts of the world. The carbonate skeleton of corals record El Niño activity by tracing sea surface temperature and salinity in the oceans where they grow. As El Niño’s core region is the equatorial Pacific Ocean, this is where the most direct consequences of ENSO are seen, commonly associated with temperature anomalies and changes in rain patterns. These changes affect the isotopic and elemental composition of surface ocean waters, which are in turn observed in corals in the affected regions. This review presents how oxygen isotope ratios (δ18O) in coral skeleton can be used as a proxy to determine climatic trends of El Niño in the past, mainly with a focus on the Holocene. I explain the main features of ENSO in the present, including its different phases and their effects. The function of corals and their oxygen isotopes is described, providing detailed information on what determines the δ18O values in seawater and carbonates, as well as the practical uses of coral δ18O and what it can tell us about paleoclimate. Further, I present and analyse the information obtained from coral δ18O on ENSO pat-terns in the past. Lastly, I suggest some improvements for future use of paleoclimatic methods for studying El Niño Southern Oscillation in order to give a more holistic understanding of past climate.
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